1. Field of the Invention
The present invention is directed to the polymerization of ethylene alone or with comonomers or telogens (modifiers) at elevated temperatures and pressures in an elongated tubular reactor. More particularly, the invention is directed to the production of solid polyethylene under conditions wherein the bulk fluid velocity is sufficiently high in the reaction zones of the tubular reactor so that the Flow Number in each reaction zone is greater than 3.3 ft..sup.2 /sec. In its more specific aspects, the invention involves the production of high quality polyethylene under conditions wherein the bulk fluid velocity is sufficiently high so that the Flow Number in each reaction zone in the tubular reactor having internal diameter between about 0.5 and 3 inches is greater than 3.3 ft..sup.2 /sec. and the effective reaction volume is increased to produce high quality polyethylene while controlling the pressure drop in the tubular reactor having at least two reaction zones so as not to exceed 6,000 and, preferably, 3,000 psi at operating pressures between 25,000 psi and 50,000 psi at the inlet of the tubular reactor as calculated or measured between the inlet of the first reaction zone and the end of the last of the reaction zones.
2. The Prior Art
The polymerization of ethylene to solid polyethylene in an elongated tubular reactor at elevated temperatures and pressures in the presence of a free radical or free oxygen yielding initiator is known. Heretofore, however, the use of high bulk fluid velocities has been carefully avoided due to the increased lengths of reaction zones thought to be necessary to accommodate the increased velocities in conventional tubular reactors. It has been understood heretofore that to provide a constant temperature rise per unit length of reaction zone in the tubular reactor, a doubling of the bulk fluid velocity would double the length of reaction zone. Hence, increasing the bulk fluid velocity in the reaction zone would necessarily increase the length thereof resulting in a much greater pressure drop occurring in the tubular reactor. In tubular reactors having one long or more than one shorter reaction zone, large pressure drops have detrimental effects on product optical property and uniformity of other physical properties since the polymer produced in the second or later portion of the reaction zone or zones are produced under lower pressures. The best film product is produced at the highest pressure. Since for practical purposes, the reaction zone must be of a finite length and increasing the length of the reaction zone increases the pressure drop, the bulk fluid velocities have not exceeded about 36 ft./sec. in a one inch pipe; i.e., a Flow Number of about 3.0.